ORCID Profile
0000-0003-1565-7323
Current Organisation
Technical University of Denmark
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Publisher: IOP Publishing
Date: 08-2019
DOI: 10.1088/1757-899X/580/1/012007
Abstract: We present an instrument for dark-field x-ray microscopy installed on beamline ID06 of the ESRF — the first of its kind. Dark-field x-ray microscopy uses full field illumination of the s le and provides three-dimensional (3D) mapping of micro-structure and lattice strain in crystalline matter. It is analogous to dark-field electron microscopy in that an objective lens magnifies diffracting features of the s le. The use of high-energy synchrotron x-rays, however, means that these features can be large and deeply embedded. 3D movies can be acquired with a time resolution of seconds to minutes. The field of view and spatial resolution can be adapted by simple reconfiguration of the x-ray objective lens, reaching spatial and angular resolution of 30-100 nm and 0.001°, respectively. The instrument furthermore allows pre-characterization of s les at larger length scales using 3DXRD or DCT, such that a region of interest (e.g. a single grain) can be selected for high-resolution studies without the need to dismount the s le. As ex les of applications we show work on mapping the subgrains in plastically deformed iron and aluminum alloys, mapping domains and strain fields in ferroelectric crystals, and studies of biominerals. This ability to directly characterize complex, multi-scale phenomena in-situ is a key step towards formulating and validating multi-scale models that account for the entire heterogeneity of materials. As an outlook, we discuss future prospects for such multi-scale characterization by combining DFXM with 3DXRD/DCT, and coherent x-ray methods for coarser and finer length-scales, respectively.
Publisher: AIP Publishing
Date: 15-11-2021
DOI: 10.1063/5.0065834
Abstract: We use dark-field x-ray microscopy to reveal evidence of subtle structural heterogeneity in BaTiO3 single crystals at temperatures of 150 °C—well above the Curie temperature of 125 °C. The heterogeneity exhibits domain-like ordering on the scale of several micrometers, pronounced curvature, and a preference for ⟨110⟩ lattice directions. Complementary high-resolution x-ray reciprocal space measurements suggest that the features originate from point defects (most likely oxygen vacancies) that coalesce along pre-existing domain walls during aging. A simple thermodynamic model suggests that the weak elastic strains associated with the heterogeneity are likely to locally raise the Curie temperature in their vicinity, creating nucleation sites for the ferroelectric phase upon cooling through the ferroelectric phase transition.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 16-07-2021
Abstract: Dark-field X-ray microscopy movies reveal how patterns of microscopic defects in bulk aluminum destabilize from 97-99% of melting.
Publisher: AIP Publishing
Date: 06-2020
DOI: 10.1063/1.5142319
Abstract: The electric-field-induced and temperature induced dynamics of domains, defects, and phases play an important role in determining the macroscopic functional response of ferroelectric and piezoelectric materials. However, distinguishing and quantifying these phenomena remains a persistent challenge that inhibits our understanding of the fundamental structure–property relationships. In situ dark field x-ray microscopy is a new experimental technique for the real space mapping of lattice strain and orientation in bulk materials. In this paper, we describe an apparatus and methodology for conducting in situ studies of thermally and electrically induced structural dynamics and demonstrate their use on ferroelectric BaTiO3 single crystals. The stable temperature and electric field apparatus enables simultaneous control of electric fields up to ≈2 kV/mm at temperatures up to 200 °C with a stability of ΔT = ±0.01 K and a r rate of up to 0.5 K/min. This capability facilitates studies of critical phenomena, such as phase transitions, which we observe via the microstructural change occurring during the electric-field-induced cubic to tetragonal phase transition in BaTiO3 at its Curie temperature. With such systematic control, we show how the growth of the polar phase front and its associated ferroelastic domains fall along unexpected directions and, after several cycles of electric field application, result in a non-reversible lattice strain at the electrode–crystal interface. These capabilities pave the way for new insights into the temperature and electric field dependent electromechanical transitions and the critical influence of subtle defects and interfaces.
No related grants have been discovered for Mustafacan Kutsal.